0019-patterns-in-function-params.md

You can use pattern matching in function parameters. examples:

struct S { 
    field1: String,
    fields2: usize,
}

fn test_fn(S { field1, .. }: S) {
    println!("{}", field1);
}


enum Id {
    V1(usize),
    V2(usize),
}

fn test_fn((Id::V1(id) | Id::V2(id)) : Id) {
    println!("{}", id);
}